A reprocessing process of collecting U237, U233 and the like from a spent nuclear fuel pin is broadly divided into wet reprocessing referred to as PUREX process using an aqueous solution based on tributyl phosphate (TBP), nitric acid or the like, and dry reprocessing using a molten salt electrolytic method. Conventionally, a spent oxide fuel pin has been processed by the wet reprocessing method. In the wet reprocessing, it is necessary to dissolve oxide fuel pellets first, and for this reason, highly acidic nitric acid has been used. However, as a result, damage such as corrosion to processing equipment is severe, and thus still no wet reprocessing facility is in commercial operation in Japan. Furthermore, operating a wet reprocessing facility requires high cost.
On the other hand, the dry reprocessing method is small scale, and thus reduction in cost is possible and critical management is easy. The dry reprocessing method is developed for metal fuel pins, and is a process of extracting U, Pu mainly from a U—Pu—Zr ternary alloy fuel pin. Also, in a fast reactor, the energy of neutrons is high, and it is not necessary to refine fuel with high purity, thus the dry reprocessing with a low purity of collected substances is likely to be applied.
In the currently studied dry reprocessing process, a fuel assembly (a bundle of fuel pins) taken out from a fast reactor is first disassembled in an “assembly disassembling process”. Subsequently, these fuel pins are sheared into short pieces of the order of several cm length in a “fuel element shear process”. The spent fuel chips obtained in this manner are dissolved in a lithium chloride-potassium chloride (LiCl—KCl) molten salt in the next “electrolytic refining process”, and actinoid elements are separated from nuclear fission products and are collected at a solid cathode or a liquid metal cadmium (Cd) cathode. A solvent such as a molten salt or liquid metal cadmium adheres to the actinoid elements collected here. Thus, these adhering substances are separated by distillation at a high temperature in a “cathode collected substance processing process”. Zirconium (Zr) or U is added to thus obtained actinoid metal to achieve a target concentration, and is melted and cast into a rod-shaped fuel alloy in an “injection molding process” at a high temperature. The fuel pin is sealed in a stainless-steel cladding tube in a “fuel element sealing process”, thereby creating a new fuel pin, which is further bundled into an assembly in an “assembly building process”, and is reloaded to a fast reactor.